Crystallite

Crystallite Structure

• Crystallites can have random or directed orientation.
• Amorphous materials lack structure.
• Polycrystalline materials are composed of multiple crystallites.
• Most inorganic solids are polycrystalline.
• Grain boundaries are the areas where crystallites meet.

Crystallite Size

• Crystallite size can be determined using X-ray diffraction or electron microscopy.
• Solid objects are rarely composed of a single crystal.
• Crystallite size can vary from nanometers to millimeters.
• Monodisperse microstructures have uniform crystallite size.
• Some materials, like gems and certain fibers, can be single crystals.

Effects on Material Physical Properties

• Crystallinity affects the physical properties of a solid.
• Different allotropic forms of sulfur have different properties.
• Powder grains can be composed of smaller polycrystalline grains.
• Polycrystals cannot be superheated and will melt promptly.
• Material fractures can be intergranular or transgranular.

Grain Boundaries

• Grain boundaries are interfaces where crystals of different orientations meet.
• Grain boundaries contain dislocations and impurities.
• Five variables are required to define a grain boundary.
• Grain boundaries disrupt the motion of dislocations.
• Reducing grain size improves strength without sacrificing toughness.

Grain Boundary Migration

• Grain boundary migration plays a role in creep mechanisms.
• Fine-grained materials have poor resistance to creep at high temperatures.
• Grain boundaries are sources and sinks of point defects.
• Migration rate in grain boundaries depends on the angle between adjacent grains.
• Grain boundaries become a significant volume fraction in nanocrystalline solids.

Crystallite Data Sources